In the ITU-R (International Telecommunication Union Radio communication sector), a standardization work for IMT (International Mobile Telecommunication)-Advanced (i.e., the next-generation mobile communication system after the third generation) is in progress. IMT-Advanced sets its goal to support Internet Protocol (IP)-based multimedia service at the data transfer rate of 1 Gbps in stop and slow-speed moving states and of 100 Mbps in a fast-speed moving state.
3GPP (3rd Generation Partnership Project) is a system standard which fulfills the requirements of IMT-Advanced, and it prepares improved LTE-Advanced (LTE-A) of LTE (Long Term Evolution) based on OFDMA (Orthogonal Frequency Division Multiple Access)/SC-FDMA (Single Carrier-Frequency Division Multiple Access) transmission schemes. The LTE-A is one of the strong candidates for IMT-Advanced. Relay node technology is included in the major technologies of the LTE-A.
A relay node is an apparatus for relaying signals between a base station and a user equipment and used to extend the cell coverage of a wireless communication system and improve the throughput.
It becomes problematic that such a relay node will demodulate a signal received from a base station using which reference signal. For example, in order for a relay node to demodulate control information of a control channel received from a base station, the relay node has to know which reference signal has been allocated to a radio resource region to which the control information is allocated.